1. Field of Invention
The present invention relates to a method for fabricating metal silicide. More particularly, the present invention relates to a method for fabricating a metal silicide film, which is capable of efficiently removing the unreacted metal alloy and residual metals.
2. Description of Related Art
Metal silicide thin films, used as ohmic contacts, Schottky barrier contacts, gate electrodes, local interconnects and diffusion barriers are commonly present in the semiconductor or microelectronics devices. For the semiconductor devices, as metal silicide has lower resistance and higher thermal stability, salicide (self-aligned silicide) technology is frequently applied to form a metal silicide layer on the surfaces of the gate and source/drain regions, in order to reduce the sheet resistance of the source/drain region and maintain the integrity of the shallow junction.
The most commonly used metal silicide materials include titanium silicide, tungsten silicide, cobalt silicide, nickel silicide, molybdenum silicide and platinum silicide. Among them, nickel-silicide (NiSi) is a promising silicide material due to its low formation temperature, low silicon consumption during silicidation and low contact resistance. However, one potential predicament for nickel-silicide is the nucleation of high resistive phase, particularly at high temperature. In order to solve the above problem, platinum (Pt) is added to the nickel-silicide and the resultant nickel-platinum (metal) silicide Ni(Pt)Si has shown enhanced functionality in sub-micron devices.
In general, a metal silicide layer is formed through the reaction of the metal with silicon at the interface between the metal layer and the gate or the source/drain regions by performing a thermal treatment toward the metal layer covering the gate electrode and/or the source/drain regions. In the process of fabricating the above metal silicide layer, the remained unreacted metal must be removed as the residual unreacted metal may negatively affect the electrical property of the device. However, take Ni—Pt metal silicide as an example, the residual platinum metal usually cannot be completely removed by using the conventional sulfuric acid-hydrogen peroxide mixture (SPM) cleaning solution or ammonium hydrogen peroxide mixture (APM) cleaning solution. As a result, extra cleaning steps or additional cleaning solutions are required for effectively removing the residual metals during the fabrication process of the metal silicide.